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THRIPS AND TOSPOVIRUSES: PROCEEDINGS OF THE 7TH INTERNATIONAL SYMPOSIUM ON THYSANOPTERA
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Predation of Frankliniella occidentalis by Orius insidiosus on plant
hosts serving as sources of populations infesting fruit orchards
Renato Ripa1, Fernando Rodriguez1, Joe Funderburk2 and Fernanda Espinoza1.
Instituto de Investigaciones Agropecuarias, Chorrillos 86, La Cruz, Chile
University of Florida, 155 Research Road, Quincy, Florida 32351 USA
E-mail: [email protected]
1
2
Summary: Annual cycles of population abundance of thrips and natural enemies were determined in
three agricultural areas in the Aconcagua valley in Central Chile. The most important plant species
serving as hosts for reproducing populations of Frankliniella occidentalis are not native to Chile. Local
populations of thrips developed year-round on Medicago sativa, Raphanus sativus, and Sisymbrium
officinale. Numbers of the predator Orius insidiosus in M. sativa were sufficient by late spring to suppress
thrips populations which persisted nearly extinct on this plant host until the winter when the predator
entered diapause. No natural enemy species reached numbers sufficient to suppress local populations
of F. occidentalis in S. officinale and R. sativus. Local populations of F. occidentalis on Eschsholzia
californica developed unchecked by natural enemies during the spring and early summer. Each of the
above-mentioned plant hosts is a source in the early spring for large numbers of F. occidentalis migrating
into nearby fruit orchards.
Key words: Frankliniella occidentalis, Orius, natural enemies, alfalfa
Introduction
The western flower thrips, Frankliniella
occidentalis, was first detected in Chile during
1995. The species is a serious pest of many crops
grown for export and domestic markets including
nectarines, peaches, grapes, peaches, peppers,
lettuce, and ornamental flowering plants. The
major agricultural areas are the valleys of central
Chile. Mass flights of F. occidentalis adults occur
in the spring when fruits and vegetables are
flowering and most vulnerable to damage. Large
plantings of alfalfa occur in the ecosystem and
several invasive plants also are common along
roadways, hedgerows, creeks, canals, and into the
hills where the soil is disturbed by grazing animals.
Alfalfa and many of the invasive plants serve as
the sources for migrating adults. We conducted
extensive surveys to determine the major plant
hosts of F. occidentalis. Cycles of population
abundance of thrips and their natural enemies on
the major plant hosts were determined, and the
importance of natural enemies was evaluated.
Material and Methods
An extensive plant survey comprising 65 plant
species was carried out on hills and valleys of
central Chile to determine the most important
hosts of western flower thrips. Plant species were
sampled in one liter glass jars partially filled with
soapy water and the thrips retrieved by filtering the
content using a set of sieves of decreasing mesh
size and examined under the stereo microscope
to determine the number of adult and larval F.
occidentalis, Thrips tabaci and Frankliniella
australis Morgan, and among natural enemies,
adults and nymphs of O. insidiosus, adults and
larvae of Aeolothrips fasciatipennis (Blanchard),
and adults of the eulophid Ceranisus menes.
Weekly samples were taken in the
following plant species: Medicago sativa,
Eschscholzia californica, Raphanus sativus,
Sysimbrium officinale, and Brassica rapa.
Samples consisted of 5 to 7 jars of 5 shoots,
inflorences, or flowers per jar with soapy water,
replicated 4 times on each date. Larval parasitism
in alfalfa was assessed by confining 20 larvae
of F. occidentalis per 15 cm Petri dish plus a
green bean pod as a food source until thrips
pupation or parasitoid emergence. Larvae were
obtained from a sample of alfalfa shoots and
placed in one paper bag per plot. A separate
set of alfalfa foliage samples was maintained
in Petri dishes so as to observe possible thrips
egg parasitoids. The importance of predators
was evaluated by determining their number in
relation to prey (Sabelis and Van Rijn 1997).
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PREDATION OF FRANKLINIELLA OCCIDENTALIS BY ORIUS INSIDIOSUS ON PLANT HOSTS SERVING AS SOURCES OF
POPULATIONS INFESTING FRUIT ORCHARDS
Results
Sampling showed that F. occidentalis was
abundant in the valleys on five common invasive
and cultivated plant species. It was not encountered
on plants growing in the hills. The important
plant species that are reproductive hosts for F.
occidentalis identified in the extensive survey were:
Medicago sativa
Cultivated crop
Eschscholzia californica
Invasive species
Raphanus sativus
Invasive species
Sisymbrium officinale
Invasive species
Brassica rapa
Invasive species
Populations of F. occidentalis were low
during the lower temperature period from April
to October (Figs. 1 and 2). Populations increased
in the spring reaching a peak in January. Larvae
were abundant on S. officinale indicating that this
plant species is a good reproductive host (Fig. 1).
Numbers of the predator O. insidiosus in relation
to prey were sufficient on many sample dates to
suppress thrips. Both E. californica and R. sativus
are poor reproductive hosts for F. occidentalis
considering the number of larvae in relation to
Figure 1. Abundance of adults and larvae of Frankliniella
occidentalis in Eschscholzia californica, Sisymbrium
officinale, and Raphanus sativus in the Aconcagua
Valley of Central Chile.
Figure 2. Annual cycle of population abundance of Frankliniella occidentalis and Orius insidiosus in the flowers and terminal
buds of Medicago sativae in the Aconcagua Valley of Central Chile.
THRIPS AND TOSPOVIRUSES: PROCEEDINGS OF THE 7TH INTERNATIONAL SYMPOSIUM ON THYSANOPTERA
adults in the samples (Fig. 1). However, both
plant species are very common, and the larvae
are able to escape predation in the near absence
of Orius. Populations of thrips in M. sativa built
to large numbers in the spring until numbers of
O. insidiosus in relation to prey were sufficient
to cause near extinction of populations (Fig. 2).
Populations of the predator in alfalfa persisted in the
near absence of prey through the summer and fall.
Ceranisus menes was collected from thrips
larvae. The parasitized larvae did not develop
wings in the prepupal stage and acquired an
orange color spot in the middle of the body. Near
to pupation the integument of the larvae opens
and the pupa of the parasitoid exits the host. The
newly emerged pupa shows an orange spot inside
the abdomen (Loomans and van Lenteren, 1995).
Adults of C. menes were found on M. sativa,
Cestrum parqui and weeds such as S. officinale
and R. sativus in unmanaged ecosystems, free of
pesticide application. Larval parasitism was very
low reaching a peak near 5% during February to
April and the lowest occured during August to
January. Such levels are considerably lower than
those reported by Loomans and van Lenteren
(1995). C. menes has several generations a year.
It completes a life cycle in about one month.
Sampling showed that A. fasciatipennis
was about 5% of the total predators collected in
alfalfa and about 15% of those in S. officinale
flowers. The low numbers of these predators
and its polyphagy suggests that it has little effect
on thrips density. No males were observed,
which suggests parthenogenetic reproduction.
No egg parasitoids or nematodes were found.
Discussion
Sabelis and Van Rijn (1997) reported the intrinsic
abilities of predators to suppress a coherent
population of F. occidentalis. Suppression by
O. insidosus was predicted at predator to prey
ratio of 1 to 217. Funderburk et al. (2000) and
Ramachandran et al. (2001) reported that field
populations in pepper were suppressed at ratios of
about 1 to 180 and that extinction occurred rapidly
when the ratio was about 1 to 40. Numbers of O.
insidiosus in relation to prey were sufficient in
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M. sativae and S. officinale on many dates during
summer and fall to predict suppression of thrips
(Figs. 1 and 2). Local extinction was evident
in M. sativa and the persistence of the predator
allowed only occasional buildup of populations.
Populations of thrips developed rapidly in
a density independent fashion during the spring
(Figs. 1 and 2). Both M. sativa and S. officinale
undoubtedly serve as major sources of thrips
invading nearby flowering crops. Although
E. californica and R. sativus may not be good
reproductive hosts for F. occidentalis, the plants
are abundant in areas of disturbed soil near crop
fields, and they may serve as important sources
for migrating adults during the spring mass
flight. Mass flights of flower thrips are typical
in the spring in temperate regions (Lewis 1997).
Funderburk et al. (2000) and Ramachandran et al.
(2001) reported that O. insidiosus is important in
the regulation of local populations and possibly
global populations during summer and fall.
We conclude that this predator is an important
natural enemy of F. occidentalis in Chile.
The only plants identified as hosts of F.
occidentalis in this study were crops and invasive
plant species. The plant species native to Chile
growing in the hills and mountains were not
found to be hosts for F. occidentalis. Agriculture
appears to be important in the persistence
and abundance of F. occidentalis in Chile.
References
Funderburk JE, Stavisky J and Olson S. 2000. Predation
of Frankliniella occidentalis (Pergande)
in field peppers by Orius insidiosus (Say).
Environmental Entomology 29, 376-382.
Loomans A and van Lenteren J. 1995. Biological
control of thrips pests: a review on thrips
parasitoids. In Biological Control ofThrips
Pests. (Loomans, A; Van Lenteren, J.;
Tommasini, M.; Maini, S.; Riudavest, J., eds)
pp. 93-180. Wageningen, Veenman Drukkers.
Ramachandran S, Funderburk JE, Stavisky J and
Olson S. 2001. Population abundance and
movement of Frankliniella species and
Orius insidiosus in field pepper. Agricultural
and Forest Entomology 3, 129-137.
Sabelis MW and van Rijn PCJ. 1997. Predation
by insects and mites. Thrips as Crop
Pests (ed. T. Lewis), pp. 259-354.
CAB International, Wallingford, UK.